The roles of cofilin and LIM-kinase in chemotaxis of phagocytes

Cofilin是一种普遍存在的肌动蛋白结合蛋白。只有未磷酸化的Cofilin才能结合肌动蛋白，并切断或解聚丝状肌动蛋白(F-Actin)，Cofilin被Cofilin的一种特殊的激酶Lim-Kinase磷酸化，成为一种不结合肌动蛋白的非活性形式。磷酸化的粘附素被一种特殊的磷酸酶--弹弓去磷酸化，成为一种活性形式。最近，我们报道了cofilin在吞噬细胞产生超氧化物和吞噬过程中的调节作用。本研究探讨了粘附素在白细胞趋化中的作用。白介素8(IL-8)是一种强有力的生理性趋化因子，它能引起cofilin的快速脱磷短链和随后的重新磷酸化。S3-R多肽可以抑制Cofilin的磷酸化，S3-R由一个膜通透性多肽和一个Cofilin磷酸化部位的多肽组成。当S3-R肽被引入中性粒细胞样HL-60细胞中时，趋化活性增强，而含有Cofilin磷酸化位点倒序的对照多肽没有这种增强作用。PI3激酶抑制剂Wortmannin和LY294002抑制Cofilin的趋化和磷酸化转换。另一方面，cofilin的siRNA导致cofilin表达下调，并抑制趋化作用。根据这些结果，我们认为未磷酸化的活性Cofilin在吞噬细胞的趋化过程中起着关键作用，而PI3-K参与了Cofilin的磷酸化/去磷酸化循环的控制。

Cofilin is a ubiquitous actin-binding protein. Only unphosphorylated cofilin binds actin and severs or depolymerizes a filamentous actin(F-actin) and cofilin is phosphrylated by LIM-kinase, a specific kinase of cofilin, to be an inactive form which does not bind actin. The phosphorylated cofilin is dephosphorylated by slingshot, a specific phosphatase, to be an active form. Recently we have reported that cofilin plays regulatory roles in superoxide production and phagocytosis by phagocytes. In this study, the roles of cofilin hi chemotaxis of leukocytes were investigated. Interleukin 8(IL-8), a potent physiological chemokine, triggered quick dephoshorylation and subsequent rephosphorylation of cofilin. The phosphorylation of cofilin was inhibited by S3-R peptide which consisted of a membrane-permeable peptide and a peptide of phosphorylation site of cofilin. When the S3-R peptide was introduced into neutrophil-like HL-60 cells, the chemotactic activity was enhanced while control peptide which contained an inverted sequence of phosphorylation site of cofilin did not such an enhancing effect. Wortmannin and LY294002,inhibitors of PI3 kinase, suppressed the chemotaxis and phosphorylation turnover of cofilin. On the other hand, siRNA of cofilin caused down-regulation of cofilin and inhibited the chemotaxis. Based on these results it is suggested that unphosphrylated active cofilin plays a critical role in the chemtaxis of phagocytes and PI3-kinase is involved in the control of phosphorylation/dephosphorylation cycle of cofilin.